Code
P1852
PORSCHE
P — Powertrain
Data bus powertrain: implausible message from engine control module
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UK: 4
EN: 9
RU: 7
AI status
Completed
Completed
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Causes
- Corroded, loose or damaged connector at the engine control module
- Broken, chafed or shorted CAN bus wiring (CAN High/CAN Low)
- Poor battery voltage or intermittent supply to the ECM (low battery, weak charging system)
- Faulty CAN transceiver inside the ECM or another module on the same bus
- Missing or incorrect software/firmware calibration or coding after a repair or update
- Incorrect network termination (missing or damaged 120Ω resistors)
Symptoms
- Malfunction Indicator Lamp (MIL) or warning lights illuminated
- Stored P1852 and often additional communication codes (U0xxx, P0600 series)
- Intermittent engine performance issues, derate, or no-start conditions if ECM messages are not received
- Loss of functions tied to engine data (cruise control, stability systems, gear shifting control in some models)
- Erratic or missing engine data on a diagnostic scanner
- Symptoms intermittent or correlated with moisture, vibration or low battery voltage
What to check
- Read and record all stored codes and freeze frame data from all control modules with a capable scan tool
- Inspect ECM and gateway connectors for corrosion, bent pins, moisture, or damage
- Check battery voltage with key-on and engine running (approx. 12.0–14.8 V). Verify charging system operation
- Visually inspect CAN High and CAN Low wiring for chafing, repairs, pinched sections, or rodent damage
- Check for other communication-related DTCs (U0100, U0073, etc.) to determine scope of bus fault
- Perform wiggle test of harnesses while monitoring live data and DTCs to reproduce fault
Signal parameters
- Typical recessive levels: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (with both ~2.5 V idle)
- Typical dominant levels: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V when messages occur; differential ≈ 2.0 V when dominant
- Expected bus termination: two 120 Ω resistors (≈60 Ω measured across CAN_H–CAN_L)
- Common CAN bus speed on powertrain network: commonly 500 kb/s (model dependent)
- ECM supply voltage expected: ~12.0–14.8 V with engine running; supply glitches or drops can cause corrupted messages
- Message periodicity: engine control messages commonly repeat every 10–100 ms depending on signal
Diagnostic algorithm
- Connect a factory-level or bi-directional scan tool and record all DTCs and live data from engine and gateway modules. Note freeze frame timestamps.
- Clear codes and attempt to reproduce. If intermittent, try with vehicle running, key cycles, and during road test where safe.
- Inspect ECM connector, engine bay harness and ground points for corrosion, bent pins, water intrusion or damage. Repair any obvious faults and retest.
- Verify battery and charging system. Repair weak charging battery or alternator issues before further network testing.
- Check for other communication codes that indicate a larger bus issue (U0100, U0073 etc.). This narrows fault location to bus or gateway area.
- Measure DC voltage on CAN_H and CAN_L with ignition on and engine off — check idle voltages near 2.5 V. If voltages are out of range, isolate and inspect harness or module transceiver.
- Measure resistance across CAN_H–CAN_L (ignition off). Expect approx. 60 Ω. Open or shorted termination will change this value.
- Use an oscilloscope or CAN analyzer to capture frames and inspect message IDs, timing and signal integrity. Look for malformed frames, missing periodic messages from the ECM, or noise spikes.
- If a single module is suspected, disconnect other non-essential modules (per manufacturer procedure) and test. Alternatively swap in a known-good module only when guided by OEM procedure and after confirming wiring integrity.
- If wiring and termination checks are good but messages remain implausible, consult technical bulletins for software updates or known ECM faults. Reflash or replace ECM only after confirming communications wiring and power/ground are correct and following Porsche-specific procedures.
Likely causes
- Corroded/loose connector at the ECM or chassis ground causing corrupted messages
- Damaged CAN bus wiring between ECM and gateway/module
- Faulty ECM CAN transceiver or internal module fault after an electrical event or software update
- Low/unstable battery voltage leading to communication errors
Fault status
Status
Powertrain data bus: implausible/invalid message detected from ECM — communication integrity fault.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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